Ink jet printing is becoming increasingly popular, particularly for so-called “desk-top publishing”, because of its capability to produce small volumes of printed matter from digital input at high throughput speeds. Recent equipment developments have led to the introduction of multi-color ink jet printers that integrate colored graphics and text. To some extent, however, the applications of ink jet printing have been limited due to the demanding requirements the ink receptors must meet in order to provide high quality text and graphics.
It is desirable that receiving media for inkjet printing are capable of absorbing significant amounts of liquid to ensure that the surface of said receptors be dry and non tacky to the touch after printing; but it is also desirable to maintain durability of printing image.
In case of multicolor ink-jet receptors, the ink-receiving layer is often subjected to multiple print, one for each primary color (yellow, magenta and cyan). During the first or second print, the amount of organic compounds absorbed in the layer can be partially desorbed creating on the image surface a local organic compound concentration that are visible as drop. Where a yellow ink is absorbed by the ink receiving layer after cyan and magenta inks have been already absorbed therein, it is possible to have the formation of yellow colored drops in specific areas on the surface of the receiving layer, areas that have been saturated with cyan and magenta inks and that are no more able to properly absorb additional inks. This problem is generally known as post printed drop sweating.
PCT Patent Application 99-06,219 describes a composition useful for surface treating a substrate for ink jet printing comprising a salt of a divalent metal being soluble in an aqueous medium at about pH 7 to about pH 9, further comprising a carrier agent and a sizing agent. Indicia printed thereon will have improved print quality characteristics.
European Patent Application 928,841 discloses an ink/media combination, in which the ink comprises an aqueous medium, a colorant and an alginic acid salt selected from the group consisting of monovalent ion salts and organic amine salts and in which the media, preferably a textile, treated with a specific water soluble salt of a metal having a valence of at least 2 produce printed chromatic images with improved bleed characteristics and sharper edges.
U.S. Pat. No. 4,649,064 discloses a rapid-drying image-recording element adapted for water-based liquid ink marking, in devices such as pen plotters, ink jet printers and the like, comprising a support having thereon a hydrophilic ink-receiving layer which is cross-linked to a degree sufficient to render it non-blocking and waterfast while permitting it to rapidly absorb a water-based liquid ink. The element is utilized in combination with a water-based liquid ink that comprises a water-dispersible cross-linkable colorant/resin composition and the ink-receiving layer contains a cross-linking agent which cross-links the colorant/resin composition, thereby rendering the ink markings smear-resistant, abrasion-resistant and waterfast.
U.S. Pat. No. 4,554,181 describes an ink jet receiving sheet having a receiving surface which includes a combination of a water soluble polyvalent metal salt and a cationic polymer, said polymer having cationic groups which are available in the receiving surface for ionically interacting with an anionic dye and insolubilizing it. Good water fastness is obtained.
JP Patent Application 59-096,988 discloses a receiving material comprising a substrate coated with layer containing a pigment, a binder and a water-soluble salt of metal having valency of at least 2 as waterproofing agent. The pigment is, for example, CaCO3, BaSO4, TiO2, and the like; the binder is, for example, oxidized starch, polyvinyl acetate latex, and the like. Decolorization or smearing of color on wetting is prevented. The water-soluble salt of metal makes color waterproof without changing the hue and improves color stability.
JP Patent Application 59-078,885 discloses an ink-jet receiving sheet having a degree of sizing of 20 seconds or less, a surface pH value between 5 and 10 and containing at least one halide, sulphate or nitrate of magnesium or calcium at a coverage of 0.1-15 g/m2. The receiving sheet has a better water resistance but does not lower the colour tone of dye.
U.S. Pat. No. 4,740,420 discloses a receiving medium for ink-jet printing comprising a support material containing at least in the surface portion thereof a water-soluble metal salt with the ion valence of the metal being 2 to 4 and a cationic organic material selected from the group consisting of alkylamine salts, quaternary ammonium salts and polyamines to improve water resistance of the printed images.
EP Patent Application 705,172 describes a receiving sheet for ink jet printing comprising a support having coated thereon one or more layers receptive for aqueous inks, said receiving sheet being characterized in that the coating comprises at least one trivalent salt of a metal of the Group IIIb of the periodic table of elements to improve water resistance. The preferred metal used in the trivalent salt is lanthanum.
Thus, there is a need for improved ink receptors that have minimum post printed drop sweating after stressed ageing, still maintaining a good glossiness.